The present invention relates to a propulsion device for a vehicle and to a method for controlling such a propulsion device.
Hybrid vehicles may be powered by a primary prime mover which may be a combustion engine, and by a secondary prime mover which may be an electrical machine. The electrical machine will be equipped with at least one battery to store electrical energy and with regulating equipment to regulate the flow of electrical energy between the battery and the electrical machine. The electrical machine may thus serve alternately as motor and generator, depending on the vehicle's operating state. When the vehicle is braked, the electrical machine generates electrical energy which is then stored in the battery. The stored electrical energy is subsequently for operation of the vehicle.
Using a conventional clutch mechanism which disconnects the gearbox input shaft from the engine during gearchange processes in the gearbox involves disadvantages, e.g. warming of the clutch mechanism's discs, resulting in greater fuel consumption and in clutch disc wear. In addition, a conventional clutch mechanism is relatively heavy and expensive. It also occupies a relatively large amount of space in the vehicle.
Connecting the engine output shaft, the electrical machine's rotor and the gearbox input shaft to a planetary gear makes it possible to dispense with the conventional clutch mechanism. Acceleration of the vehicle will deliver increased torque from the engine and the electrical machine to the gearbox and thence to the vehicle's powered wheels. The fact that both the engine and the electrical machine are connected to the planetary gear means that the maximum torque deliverable by the engine and the electrical machine will be limited by whichever of these prime movers has lower maximum torque than the other. Should the maximum torque of the electrical machine be lower than that of the engine, the electrical machine will not be able to generate sufficient reaction torque to the planetary gear, with the result that the engine cannot transmit its maximum torque to the gearbox and thence to the vehicle's powered wheels. The maximum torque transferrable to the gearbox is therefore limited by the power of the electrical machine. In particular, when powerful acceleration of the vehicle is desired and the electrical machine cannot generate sufficient reaction torque, undesirable heat will be generated in the electrical machine.
Specification US-A1-2003/0078127 refers to a propulsion system for a vehicle with a combustion engine and an electric motor which are connected to a planetary gear. The planetary gear's planet wheel carrier is connected to an input shaft of a gearbox. The planet wheel carrier and the planetary gear's sunwheel can be firmly connected by a sleeve so that the electrical machine and the gearbox input shaft can rotate as a fixed rotating unit.
The space available for the propulsion device in a vehicle is often limited. If the propulsion device comprises a plurality of components, e.g. a combustion engine, an electrical machine, a gearbox and a planetary gear, the configuration needs to be compact. For this reason it is desired that the dimensions of the electrical machine be small, which limits its power and maximum possible torque generation.
The components of the propulsion device are also required to be of high reliability and high operational safety and be capable of transmitting a large torque while at the same time having small dimensions and low weight.